Pressure regulating valves are used in a wide variety of industrial and residential applications for controlling the downstream pressure of a fluid. For example, in chemical processing plants or oil refineries, pressure regulating valves are used to manipulate a fluid flowing within the system to compensate for increases or decreases in demand or other load disturbances, and thus control the pressure of the fluid within a desired range. Generally speaking, when the downstream demand increases, a pressure regulating valve opens to allow more fluid to flow through the valve to the downstream portion of the system, thus maintaining a relatively constant downstream pressure. On the other hand, when the downstream demand decreases, the pressure regulating valve closes to reduce the amount of fluid flowing through the valve, again maintaining a relatively constant downstream pressure.
On the other hand, a back-pressure regulating valve operates on different principles. Whereas the above-mentioned pressure regulators regulate the fluid pressure on the downstream side of the valve, a back-pressure regulator controls the pressure on the upstream side of the valve. Consequently, a back-pressure regulator opens when the pressure on the inlet or upstream side exceeds a set point.